The present invention relates to a roll media feed apparatus for us in, for example, a copier, plotter or printer environment and more particularly to a detection system which provides an indication that the roll media supply is near exhaustion.
Various image recording systems enable a paper feeding function by feeding paper from a roll and cutting the paper into desired lengths upstream of the paper feed station. Typically, the media (paper, vellum, etc.) is wound about a core which supports the media and permits the media roll to be unwound and sheets are cut therefrom. A conventional sheet handling apparatus unrolls the media from the supply roll and advances a selected length to the sheet cutter station. A machine control system integrates and synchronizes operation of the feeding and cutting system as well as the overall machine operation.
A problem of prior art roll media type systems relates to conditions which arise when the media runs out and is exhausted from the supply roll. Typically, the trail edge of the roll media is actually glued to its cardboard tube core. This poses a threat of damaging or stalling the registration and feeding hardware if the cardboard tube were to be pulled up into the bypass area of the machine. Also, as the roll unwinds and reaches the end of the supply, the media advance is halted and a stalling condition occurs. The stalling can occur at any point along the path of the media including stations where an image is transferred to the media and/or fused. The stalling action can result in damage occurring to, for example, a fuser roll applicator where stripper fingers are used to detach the media from the fuser roll. If the media is stalled, the stripper fingers tend to score the surface of the roll, a condition referred to in the art as "skiving". Continued skiving leads to failure of and replacement of the fuser roll.
One prior art effort to solve this out of media problem is disclosed in U.S. Pat. No. 4,885,613. Disclosed therein is a roll media supply system where an end of media is detected by means of a sensor arrangement shown in FIGS. 3C and described in Col. 4, lines 45-69. An arm 61 rides along the surface of media roll 11. Arm 61 is mechanically coupled to a pivotable plate 64 whose instant position is a function of the roll 11 diameter. Plate 64 overlies a group of five sensors S11. As the diameter of roll 11 is reduced during operation as the media unrolls, successive sensors are exposed to light until a last sensor associated with the end of media provides a signal indicative of such playout. The signals from the last sensor are used to switch operation from the roll media nearing playout to another roll media which has additional remaining paper. Additional signals are generated to control the sheet cutting operation. If all media rolls are exhausted, a copy operation inhibition signal is generated (col. 17, lines 39-60). This type of solution can be characterized as a "low media" remedy; additional media may still be available for copier purposes.
Another solution is embodied in a detection circuitry within the Xerox 3050 large document copier. This machine transfers developed images onto a media such as plain paper or vellum supplied from one of three rolls. Each roll has an encoder coupled to the media roll shaft. The encoder, and related logic, monitor encoder transitions at sample time periods. An increase in the number of transitions per selected time period provides an indication that the media supply is running low but it is not precisely enough to warrant halting copy operations since 10-20 feet of media may still be available for copying purposes and operation typically continues. The above-mentioned solutions do not completely solve the problem since lifting of the media core into the bypass area could still occur.